import React, { Component } from 'react'

export default class App extends Component {
  state = { a: 1}
  render() {
    return (
      <div>
        <button onClick = {() => {
          this.setState((prevState) => {
            return {
              a: prevState.a + 10 
            }
          })
        }}>{ this.state.a }</button>
      </div>
    )
  }
}
